This invention is generally directed to titanyl phthalocyanines and processes for the preparation thereof, and more specifically, the present invention is directed to processes for obtaining the Type I polymorph of titanyl phthalocyanine with a more perfect crystalline form, and layered photoconductive members comprised of the aforementioned titanyl phthalocyanine polymorph. The more perfect crystalline structure of the Type I polymorph of titanyl phthalocyanine is differentiated from the less perfect crystalline forms of the same polymorph primarily on the basis of its characteristic X-ray powder diffraction pattern, by its characteristic Raman spectrum and by its enhanced xerographic photosensitivity and stability when compared to a number of the prior art Type I polymorphs of titanyl phthalocyanine. The titanyl phthalocyanine photogenerator pigments with enhanced performance in layered photoconductive members can be obtained by decreasing the level of inherent crystal defects and dislocations in the fundamental crystallite. These defects can be probed and characterized spectroscopically by techniques such as X-ray powder diffraction spectroscopy and Raman spectroscopy. In one embodiment, the process of the present invention comprises the dissolution of a known Type I titanyl phthalocyanine in a trihaloacetic acid and an alkylene halide; reprecipitating the dissolved pigment in a nonsolvent, for example an alcohol or water, or mixtures thereof, to provide Type X titanyl phthalocyanine; separating the Type X titanyl phthalocyanine therefrom; treating the Type X with a halobenzene to obtain a Type IV titanyl phthalocyanine; and subsequently treating by, for example, stirring or milling the Type IV with a dihaloalkane, such as dichloromethane, to form a Type I titanyl phthalocyanine with a more perfect crystal structure as evidenced by X-ray powder diffraction, which crystal structure is different from that of the initial Type I titanyl phthalocyanine precursor. Layered imaging members containing the Type I obtained by the processes of the present invention possess a number of advantages, such as enhanced photoconductivity, reduced dark decay, and very low, for example from about 3 to about 5 percent, cycle down after 50,000 xerographic imaging cycles, together with improved electrical stability. In an embodiment, the process of the present invention comprises the preparation of the precursor Type I polymorph titanyl phthalocyanine by the reaction of titanium tetra(alkoxide) with diiminoisoindolene in a solvent such as chloronaphthalene. Thereafter, the precursor Type I obtained is dissolved in a solvent mixture of trifluoroacetic acid and methylene chloride; and thereafter, the dissolved pigment is precipitated by, for example, adding with stirring the aforementioned mixture to a mixture of methanol and water, separating the product Type X phthalocyanine therefrom by, for example, filtration, slurrying and mixing the product obtained with chlorobenzene to obtain Type IV titanyl phthalocyanine. The Type IV obtained is subsequently treated in slurry form with dichloromethane by, for example, stirring or milling to enable a Type I titanyl phthalocyanine with a lower level of crystalline defects, or a more perfect crystal structure, when compared to the precursor Type I titanyl phthalocyanine. The titanyl phthalocyanine Type I obtained can be selected as an organic photogenerator pigment in photoresponsive imaging members containing charge transport, especially hole transport, layers such as those containing aryl amine hole transport molecules. The aforementioned photoresponsive imaging members can be negatively charged when the photogenerating layer is situated between the hole transport layer and the substrate, or positively charged when the hole transport layer is situated between the photogenerating layer and the supporting substrate. The layered photoconductor imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible with toner compositions of the appropriate charge. Generally, the imaging members are sensitive in the wavelength regions of from about 600 to about 850 nanometers, thus inexpensive solid state diode lasers can be selected as the light source.
Many processes for the preparation of titanyl phthalocyanines are known, such as the sulfuric acid pasting methods, reference for example EPO publication 314,100. In the aforementioned Mita EPO Patent Publication 314,100, there is illustrated the synthesis of titanyl phthalocyanine, see for example pages 5 and 6, by, for example, the reaction of titanium alkoxides and diiminoisoindolene in quinoline or an alkylbenzene, and the subsequent conversion thereof to an alpha Type pigment (Type II) by an acid pasting process, whereby the synthesized pigment is dissolved in concentrated sulfuric acid, and the resultant solution is poured onto ice to precipitate the alpha-form, which is filtered and washed with methylene chloride. This pigment, which was blended with varying amounts of metal free phthalocyanine, could be selected as the electric charge generating layer in layered photoresponsive imaging members with a high photosensitivity at, for example, 780 nanometers.
In Japanese 62-256865, there is disclosed, for example, a process for the preparation of pure Type I involving the addition of titanium tetrachloride to a solution of phthalonitrile in an organic solvent which has been heated in advance to a temperature of from 160.degree. to 300.degree. C. In Japanese 62-256866, there is illustrated, for example, a method of preparing the aforementioned polymorph which involves the rapid heating of a mixture of phthalonitrile and titanium tetrachloride in an organic solvent at a temperature of from 100.degree. to 170.degree. C. over a time period which does not exceed one hour. In Japanese 62-256867, there is described, for example, a process for the preparation of pure Type II (B) titanyl phthalocyanine, which involves a similar method to the latter except that the time to heat the mixture at from 100.degree. to 170.degree. C. is maintained for at least two and one half hours. Types I and II, in the pure form obtained by the process of the above publications, apparently afforded layered photoresponsive imaging members with excellent electrophotographic characteristics. Also, as mentioned in the textbook Phthalocyanine Compounds by Moser and Thomas, the disclosure of which is totally incorporated herein by reference, polymorphism or the ability to form distinct solid state forms is well known in phthalocyanines. For example, metal-free phthalocyanine is known to exist in at least 5 forms designated as alpha, beta, pi, X and tau. Copper phthalocyanine crystal forms known as alpha, beta, gamma, delta, epsilon and pi are also described. These different polymorphic forms are usually distinguishable on the basis of differences in the solid state properties of the materials, which can be determined by measurements, such as Differential Scanning Calorimetry, Infrared Spectroscopy, Ultraviolet-Visible-Near Infrared spectroscopy and, especially, X-ray Powder Diffraction techniques. There appears to be general agreement on the nomenclature used to designate specific polymorphs of commonly used pigments such as metal-free and copper phthalocyanine. However, this does not appear to be the situation with titanyl phthalocyanines as different nomenclature is selected in a number of instances. For example, reference is made to alpha, beta, A, B, C, y, and m forms of TiOPc (titanyl phthalocyanine) with different names being used for the same form in some situations. It is believed that five main crystal forms of TiOPc are known, that is Types X, I, II, III, and IV.
TABLE 1 ______________________________________ Crystal Other Form Names Documents ______________________________________ Type I .beta. Toyo Ink Electrophotog. (Japan) 27, 533 (1988) .beta. Dainippon U.S. Pat. No. 4,728,592 .beta. Sanyo-Shikiso JOP 63-20365 A Mitsubishi JOP 62-25685, -6, -7 Conference Proceedings A Konica "Japan Hardcopy 1989", 103, (1989) Type II .alpha. Toyo Ink "Electrophoto (Japan)" 27, 533 (1988) .alpha. Sanyo-Shikiso JOP 63-20365 .alpha. Konica U.S. Pat. No. 4,898,799 .alpha. Dainippon U.S. Pat. No. 4,728,592 .alpha. Mita EU 314,100 B Mitsubishi JOP 62-25685, -6, -7 B Konica "Japan Hardcopy 1989, 103, (1989) Type III C Mitsubishi OP 62-25685, -6, -7 C Konica "Japan Hardcopy 1989, 103, (1989) m Toyo Ink "Electrophoto (Japan)" 27, 533 (1988) Type IV y Konica "Japan Hardcopy 1989", 103, (1989) Unnamed Konica U.S. Pat. No. 4,898,799 New Type Sanyo-Shikiso JOP 63-20365 ______________________________________
The aforementioned documents illustrate, for example, the use of specific polymorphs of titanyl phthalocyanine in electrophotographic devices.
In U.S. Pat. No. 4,664,997, there is illustrated a process for the preparation of the Type I polymorph of titanyl phthalocyanine, wherein the polymorph produced exhibits peaks in the X-ray powder diffraction pattern at Bragg angles (2 theta) between 4 and 8 degrees that are stipulated to be less than 5 percent of the intensity of the diffraction peak at Bragg angle 26.3 degrees. A lengthy process is described, for example columns 8 and 9, wherein titanyl phthalocyanine of the Type I polymorph is prepared by the reaction of titanium tetrachloride with phthalonitrile at 200.degree. C. in chloronaphthalene as a solvent. The crude product obtained is purified extensively by washing with first, chloronaphthalene, then methanol, and hot water. The resultant pigment is then suspended, filtered, and resuspended in hot N-methyl pyrrolidone for 5 consecutive slurries, followed by extensive further washings with methanol. This procedure appears to provide a method for purification of Type I titanyl phthalocyanine by removing small amounts of a contaminant Type II titanyl phthalocyanine present in the crude Type I titanyl phthalocyanine. This is evident from a consideration of the X-ray diffraction patterns depicted in FIGS. 5, 6, and 7 of U.S. Pat. No. 4,664,997, which show the presence of small amounts of Type II titanyl phthalocyanine, as evidenced by the small peak at Bragg angle (2 theta) at 7.5 degrees. It is the removal of this contaminant Type II titanyl phthalocyanine, which apparently leads to the improved electrophotographic performance depicted in Table I of U.S. Pat. No. 4,664,997, as a result of the improved washing procedures as described in Preparation Examples 1, 2, 3, and 4 of the aforementioned U.S. Pat. No. 4,664,997. No evidence is provided in U.S. Pat. No. 4,664,997 that indicates that a more perfect crystalline form of the Type I polymorph of titanyl phthalocyanine had been prepared. The X-ray powder diffraction pattern for the preferred embodiment, depicted in FIG. 1 of this patent, does not show the small peak at Bragg angle 6.8.degree.; nor does it show the dramatically enhanced intensity of the peaks at Bragg angle (2 theta) at 9.2.degree., 10.4.degree., 13.1.degree., 15.0.degree., 15.6.degree., and 16.0.degree., relative to the most intense peak at 26.2.degree.; neither does it show the resolved peak at 26.5.degree. as claimed in the present invention. Compare, for example, FIG. 1 of U.S. Pat. No. 4,664,997 and FIG. 1 of the present invention.
In Sanyo-Shikiso Japanese 63-20365/86, reference is made to the known crystal forms alpha and beta TiOPc (Types II and I, respectively, it is believed), which publication also describes a process for the preparation of a new form of titanyl phthalocyanine. This publication appears to suggest the use of the unnamed titanyl phthalocyanine as a pigment and its use as a recording medium for optical discs. This apparently new form was prepared by treating acid pasted TiOPc (Type II form, it is believed) with a mixture of chlorobenzene and water at about 50.degree. C. The resulting apparently new form is distinguished on the basis of its XRPD, which appears to be identical to that shown in FIG. 3 for the Type IV polymorph.
In U.S. Pat. No. 4,728,592, there is illustrated, for example, the use of alpha type TiOPc (Type II) in an electrophotographic device having sensitivity over a broad wavelength range of from 500 to 900 nanometers. This form was prepared by the treatment of dichlorotitanium phthalocyanine with concentrated aqueous ammonia and pyridine at reflux for 1 hour. Also described in the aforementioned patent is a beta Type TiOPc (Type I) as a pigment, which is believed to provide a much poorer quality photoreceptor.
In Konica Japanese 64-17066/89, there is disclosed, for example, the use of a new crystal modification of TiOPc prepared from alpha type pigment (Type II) by milling it in a sand mill with salt and polyethylene glycol. This pigment had a strong XRPD peak at a Bragg Angle (2 theta) value of 27.3 degrees. This publication also discloses that this new form differs from alpha type pigment (Type II) in its light absorption and shows a maximum absorbance at 817 nanometers compared to alpha type, which has a maximum at 830 nanometers. The XRPD shown in the publication for this new form is believed to be identical to that of the Type IV form previously described by Sanyo-Shikiso in JOP 63-20365. The aforementioned Konica publication also discloses the use of this new form of TiOPc in a layered electrophotographic device having high sensitivity to near infrared light of 780 nanometers. The new form is indicated to be superior in this application to alpha type TiOPc (Type II). Further, this new form is also described in U.S. Pat. No. 4,898,799 and in a paper presented at the Annual Conference of Japan Hardcopy in July 1989. In this paper, this same new form is referred to as Type y, and reference is also made to Types I, II, and III as A, B, and C, respectively.
In the journal, Electrophotography (Japan) vol. 27, pages 533 to 538, Toyo Ink Manufacturing Company, there are disclosed, for example, alpha and beta forms of TiOPc (Types II and I, respectively, it is believed) and also this journal discloses the preparation of a Type M TiOPc, an apparently new form having an XRPD pattern which was distinct from other crystal forms. It is believed that this XRPD is similar to that for the Type III titanyl phthalocyanine pigment but it is broadened most likely as the particle size is much smaller than that usually found in the Type III pigment.
Processes for the preparation of specific polymorphs of titanyl phthalocyanine, which require the use of a strong acid such as sulfuric acid, are known, and these processes, it is believed, are not easily scalable. One process as illustrated in Konica Japanese Laid Open on Jan. 20, 1989 as 64-17066 (U.S. Pat. No. 4,643,770 appears to be its equivalent), the disclosure of which is totally incorporated herein by reference, involves, for example, the reaction of titanium tetrachloride and phthalonitrile in 1-chloronaphthalene solvent to produce dichlorotitanium phthalocyanine which is then subjected to hydrolysis by ammonia water to enable the Type II polymorph. This phthalocyanine is preferably treated with an electron releasing solvent, such as 2-ethoxyethanol, dioxane, or N-methylpyrrolidone, followed by subjecting the alpha-titanyl phthalocyanine to milling at a temperature of from 50.degree. to 180.degree. C. In a second method described in the aforementioned Japanese Publication, there is disclosed the preparation of alpha type titanyl phthalocyanine with sulfuric acid. Another method for the preparation of Type IV titanyl phthalocyanine involves the addition of an aromatic hydrocarbon, such as chlorobenzene solvent, to an aqueous suspension of Type II titanyl phthalocyanine prepared by the well known acid pasting process, and heating the resultant suspension to about 50.degree. C. as disclosed in Sanyo-Shikiso Japanese 63-20365, Laid Open in Jan. 28, 1988. In Japanese 171771/1986, Laid Open Aug. 2, 1986, there is disclosed the purification of metallophthalocyanine by treatment with N-methylpyrrolidone.
To obtain a titanyl phthalocyanine based photoreceptor having high sensitivity to near infrared light, it is believed necessary to control not only the purity and chemical structure of the pigment, as is generally the situation with organic photoconductors, but also to prepare the pigment in the preferred crystal modification. The disclosed processes used to prepare specific crystal forms of TiOPc, such as Types I, II, III and IV, are either complicated and difficult to control, as in the preparation of pure Types I and II pigment by careful control of the synthesis parameters by the processes described in Mitsubishi Japanese 62-25685, -6 and -7; involve harsh treatment such as sand milling at high temperature, reference Konica U.S. Pat. No. 4,898,799; or dissolution of the pigment in a large volume of concentrated sulfuric acid, a solvent which is known to cause decomposition of metal phthalocyanines, reference Sanyo-Shikiso Japanese 63-20365 and Mita EPO 314,100.
Generally, layered photoresponsive imaging members are described in a number of U.S. patents, such as U.S. Pat. No. 4,265,900, the disclosure of which is totally incorporated herein by reference, wherein there is illustrated an imaging member comprised of a photogenerating layer and an aryl amine hole transport layer. Examples of photogenerating layer components include trigonal selenium, metal phthalocyanines, vanadyl phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006 a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in the '006 patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles.
In a copending application U.S. Ser. No. 537,714 (D/90087), the disclosure of which is totally incorporated herein by reference, there are illustrated photoresponsive imaging members with photogenerating titanyl phthalocyanine layers prepared by vacuum deposition. It is indicated in this copending application that the imaging members comprised of the vacuum deposited titanyl phthalocyanines and aryl amine hole transporting compounds exhibit superior xerographic performance as low dark decay characteristics result and higher photosensitivity is generated, particularly in comparison to several prior art imaging members prepared by solution coating or spray coating, reference for example U.S. Pat. No. 4,429,029 mentioned hereinbefore.
In U.S. Pat. No. 5,153,313 (D/90244), the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of phthalocyanine composites which comprises adding a metal free phthalocyanine, a metal phthalocyanine, a metalloxy phthalocyanine or mixtures thereof to a solution of trifluoroacetic acid and a monohaloalkane; adding to the resulting mixture a titanyl phthalocyanine; adding the resulting solution to a mixture that will enable precipitation of said composite; and recovering the phthalocyanine composite precipitated product.
In U.S. Pat. No. 5,166,339 (D/90198), the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of titanyl phthalocyanine Type I, Type II, Type III, Type IV, Type X, Type Z-1, and Type Z-2, which consists essentially of dissolving a titanyl phthalocyanine in a solution of trifluoroacetic acid and methylene chloride; adding the resultant solution to a solvent or solvent mixture that will enable precipitation; and separating the product titanyl phthalocyanine from the solution followed by an optional washing; and in U.S. Pat. No. 5,164,493 (D/90524), the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of titanyl phthalocyanine Type I consisting essentially of the addition of titanium tetraalkoxide to a mixture of phthalonitrile and a diiminoisoindoline to a solvent of N-methylpyrrolidone, chloronaphthalene, chlorobenzene, or quinoline, followed by heating, and wherein the alkoxide contains from 1 to about 6 carbon atoms.
In U.S. Pat. No. 5,206,359 there is disclosed a process for the preparation of titanyl phthalocyanine which comprises the treatment of titanyl phthalocyanine Type X with a halobenzene; U.S. Pat. No. 5,189,156 discloses a process for the preparation of titanyl phthalocyanine which comprises the reaction of a titanium tetraalkoxide and diiminoisoindolene in the presence of a halonaphthalene solvent; dissolving the resulting Type I titanyl phthalocyanine in a haloacetic acid and an alkylene halide; adding the resulting mixture slowly to a cold alcohol solution; and thereafter isolating the resulting Type X titanyl phthalocyanine; slurrying the resultant Type X titanyl phthalocyanine in a halobenzene solvent, such as chlorobenzene, to give Type IV titanyl phthalocyanine with an average volume particle size diameter of from about 0.01 to about 0.1 micron; U.S. Pat. No. 5,189,155 discloses a process for the preparation of titanyl phthalocyanine Type I which comprises the reaction of titanium tetraalkoxide and diiminoisoindolene in the presence of a halonaphthalene solvent; and U.S. Pat. No. 5,182,382 illustrates processes for the preparation of titanyl phthalocyanines and photoresponsive imaging members thereof. More specifically, in one embodiment of this copending application there are provided processes for the preparation of titanyl phthalocyanine (TiOPc) Type X polymorphs which comprises the solubilization of a titanyl phthalocyanine Type I, which can be obtained by the reaction of diiminoisoindoline and titanium tetrabutoxide in the presence of a solvent, such as chloronaphthalene, reference U.S. Pat. No. 5,189,156, the disclosure of which is totally incorporated herein by reference, in a mixture of trifluoroacetic acid and methylene chloride, precipitation of the desired titanyl phthalocyanine Type X, separation by, for example, filtration, and thereafter subjecting the product to slurrying in fluorobenzene to provide Type X TiOPc exhibiting xerographic characteristics which are superior to those of the Type X formed prior to the fluorobenzene treatment. The product can be identified by various known means including X-ray powder diffraction (XRPD).
The disclosures of each of the aforementioned patents are totally incorporated herein by reference.